1. Field of the Disclosure
Various embodiments of the present disclosure relate generally to interference cancellation for a communication device in a cellular communication system, and more particularly, to a scheme for blind detecting a transmission mode of an interference signal.
2. Description of the Related Art
To satisfy strict requirements of the international telecommunication union radio communication Sector (ITU-R), next-generation cellular networks, such as, for example, long term evolution-advanced (LTE-A), have been designed that support a broad bandwidth having a maximum of 100 MHz for up to 8 layers in a downlink (DL) and up to 4 layers in an uplink (UL), through higher-order spatial multiplexing and carrier aggregation (CA).
However, spatial frequency reuse using more cells provides a capacity gain that is greater than a case with one cell having an increased spatial order or spectrum bandwidth. Hence, heterogeneous networks using small cells in a macro-cell environment have emerged as a development path for the next-generation cellular networks.
Although heterogeneous networks offer various benefits, they may also bring about an unprecedented challenge to cellular networks. Interference management, which is a matter of great concern (like the number of base stations (BSs)) is significantly increased. In this context, advanced co-channel interference aware signal detection has attracted attention in a recent development process for the LTE-A systems. When cells are deployed very densely in heterogeneous networks, inter-cell interference becomes worse, causing significant issues in cellular networks.
Various attempts have been made to solve the above-described problems.
Enhanced inter-cell interference coordination (eICIC) has been proposed to mitigate interference of a macro cell with respect to a user equipment (UE) located closer to small cells.
In addition, the concept of an almost blank subframe (ABS) has been introduced as a BS-based interference mitigation scheme. In a subframe indicated as an ABS, by a BS, a macro cell may mitigate interference by avoiding transmission in a DL data channel, such as, for example, a physical downlink shared channel (PDSCH), except for pilot signals (e.g., cell-specific reference signals (CRSs)).
UE-based interference mitigation using recognition of a CRS sequence has also been considered. Further enhanced inter-cell interference coordination (FeICIC) permitting CRS interference cancellation (CRS-IC) by a UE has been established by LTE Release 11 of the 3rd generation partnership project (3GPP).
Moreover, network-assisted interference cancellation and suppression (NAICS) has been studied by the 3GPP. A work item, referred to as NAICS, is being standardized and approved in LTE Release 12. It has become apparent from the study that a significant performance gain can be achieved on the assumption that interference parameters are known to a UE through broadcasting or dedicated signaling (e.g., higher-layer signaling like radio resource control (RRC) signaling), or newly defined downlink control information (DCI). However, the success of NAICS based on signaling depends on the use of signaled parameters (e.g., a rank indicator (RI), a precoding matrix indicator (PMI), and a modulation level (MOD)) by interfering BSs, potentially limiting scheduling flexibility for neighboring cells. Moreover, the support of interference parameters is not applied at all times in real systems, because a backhaul capacity between BSs and the capacity of control channels from the BS to the UE are generally limited.
To overcome the cell scheduling limitation and the network signaling overhead, the UE may blindly estimate interference parameters from received signals. Joint blind detection (BD) of an RI, a PMI, and a MOD may utilize a maximum likelihood (ML) estimation including an exhaustive search in all possible combinations of Ms, PMIs, and MODs designated in LTE systems. In LTE-orthogonal frequency division multiple access (LTE-OFDMA) systems, for UEs that are scheduled at the same time, assigned RI, PMI, and MOD may vary from one transmission time interval (TTI) to another TTI in a time domain, and from one resource block (RB) to another RB in a frequency domain. This means that joint BD is required to be performed for each RB in every TTI in LTE DL systems.
However, this assumption also means that the interference parameters may dynamically change from one RB of the frequency domain to another RB in every TTI according to channel conditions, which limits scheduling performance and excessively increases the network signaling load.
Furthermore, a need arises to solve an interference issue for LTE DL normal subframes including traffic signals, as well as pilot signals (e.g., a CRS).